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Loose ends
Just to pick up on some bits and pieces discussed in this thread:
Variable ND filters
Variable ND filters made from crossed polarizers are not visually safe (I think they pass too much IR) and probably won't give sufficient ND for solar photography. They only go down to a few % transmission. A solar filter is 0.01% to 0.001%. I am assuming you were talking about using them for the partial phases.
If you were thinking of using them for totality, I recommend against this. It's unnecessarily complicating things AND the corona is polarized so as you rotate the filters, different streamers will come into view. you will have a very hard time trying to stack and radially merge these images to make a composite or HDR image.
Using Auto exposure
Works really well for wide field exposures - wider than 28mm where you are trying to capture sky and landscape. It does not work for close ups of the eclipse and corona. At ISO100 & at f8 the inner corona needs about 1/4000. Then just keep increasing the exposure to about 4s to capture out to about 8 solar radii. Note that sky conditions may be brighter than the brightness of the corona at 8 Rs.
Colour of Sun with Baader film
Pictures taken with Baader film can be easily recoloured to any colour.
Filter types
Glass filters are not much good for eclipse photography because you have to refocus for totality after removing them. The Baader film is so thin that the focus remains unchanged. When removed 10-15s before you really don't want to be mucking around with focus.
Baader 48mm filter?
I think you're referring to the Baader solar continuum filter which gives a green image. It must be used with a full ND filter 4 or above and would be difficult to remove before totality, unless you have it on a separate optical system that you won't use during totality. It gives better definition for solar surface detail.
Ideal focal length or field of view
There isn't one. There are reasons for using short, medium and long focal lengths. In my reading of the posts, some writers seem to be thinking about this in terms of photographing the 30 arc minute disc of the Moon. You are not. The corona extends out to to 20 or more degrees diameter. Look at the C3 coronagraph images. I saw 7 degrees of corona visually when at high altitude in November 1994. It has been captured photographically during an eclipse out to about 13 degrees. You need to decide what of the many phenomena you are trying to capture and then decide on the best image scale to capture it.
Mithrandir wrote "2000mm would give you a sun that almost filled the frame." This is true but only if you center the sun in the field. You don't have to. If you are trying to capture inner corona in great detail, you can offset the sun to the edge of field and pick up nearly 1 - 2 solar radii of inner corona.
Conclusion
Whatever you do, don't leave yourself anything to do apart from removing a solar filter during the last 30s before totality. There is so much going on around you, it's not the time to be staring into a camera. Keep it nice and simple.
Joe Cali
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